Navigate to your Job > Job Financials > Change Orders and open the relevant change order or click 
to create.
Use the Link to selection set drop-down to select your desired selection set. Ensure the set has no entered costs, as any approved sets with allocated costs differing from the allowance or budget will automatically create a change order.
Once the change order is linked to a selection set, it cannot be approved or declined until the status of the linked change order is either approved or declined.
For more information on how variations are automatically created with a new selection set, see this article.